FLUORESCENCE STUDY OF THE BINDING OF M7GPPPG AND RABBIT GLOBIN MESSENGER-RNA TO PROTEIN-SYNTHESIS INITIATION FACTOR-4A, FACTOR-4E, AND FACTOR-4F

The interactions of protein synthesis initiation factors eIF-4E from human erythrocytes and eIF-4A and eIF-4F from rabbit reticulocytes with the cap analogue m7GpppG and rabbit globin mRNA were investigated. The equilibrium binding constants for the binary complex formation of eIF-4E-eIF-4A, m7GpppG-eIF-4E, m7GpppG-eIF-4F, globin mRNA-eIF-4E, globin mRNA-eIF-4F, and globin mRNA-eIF-4A were measured by direct fluorescence titration experiments. The binding of eIF-4E to globin mRNA was found to be 5.5-fold tighter than its binding to m'GpppG; the binding of eIF-4F for globin mRNA and m7GpppG was similar to that of eIF-4E. Association equilibrium constants were determined for the ternary system mRNA-eIF-4E-eIF-4A; four thermodynamically independent equilibria characterize the system. These equilibrium binding constants were used to calculate coupling free energies, which provided an estimate of the cooperativity of the interaction of eIF-4E, eIF-4A, and mRNA. These coupling energies were all found to be small and positive, indicative of anticooperative binding. © 1990 American Chemical Society. All rights reserved.